1. Field of the Invention
This invention relates to a snowmobile with a long track designed to provide improved traction and smoother ride in light or powder snow. Further, the present invention concerns a new tread pattern of a snowmobile drive track wherein, among others, the track provides superior flotation and traction while maintaining an acceptable degree of maneuverability compared to the conventional track tread patterns in light or powder snow.
2. Description of Related Art
Given the popularity of snowmobiles nowadays, snowmobile manufacturers are offering increasingly diverse choices of snowmobiles adapted for use in different environments. Examples of various categories of snowmobiles include, inter alia, high-performance snowmobiles, touring snowmobiles, utility snowmobiles, and mountain snowmobiles. The mountain snowmobiles, in particular, are designed to meet the unique demands required by the driving conditions in both the mountains and the trails. Such driving conditions include climbing hills, maneuvering sharp turns around trees, and riding on deep powder snow.
Hill climbing refers to driving a snowmobile up the slopes of the mountains. This task requires that the track of the sled to provide greater traction than as would be provided by the tracks for flatland snowmobiles. More specifically, when climbing hills or sidehilling, the mountain sled is driven in a crisscrossing fashion, substantially upwardly in diagonal directions of the hills, intermittently reversing the lateral direction of the travel. During this operation, the weight of the sled plus the driver is shifted substantially from one lateral side to another, and the sled may be operating substantially leaning on one side. Such sidehilling maneuvers require the snow engaging lugs of both lateral sides of the track to provide substantially more traction than the flatland counterparts. To provide more traction force than the flatland snowmobiles, the mountain snowmobiles typically use longer tracks which have snow engaging lugs with higher heights. Accordingly, where the typical height of the snow engaging lugs for the tracks of flatland snowmobiles is less than about 1 inches, the height of the snow engaging lugs for the mountain snowmobiles is greater than about 1¼ inches, preferably in the range of about 1¾ inches to 2 inches.
Acceptable maneuverability of the snowmobiles during sharp turns is another key ingredient of a mountain snowmobile. Driving the snowmobiles in the mountains frequently requires making turns, particularly in heavily wooded areas, and the mountain snowmobiles should be designed to maintain the steerability of the sleds. While the increased traction force provided by the tracks with higher heights of the snow engaging lugs and the longer nominal length provides improved traction in hill climbing, such tracks tend to propel or “push” the sleds too much, thereby overwhelming the mountain snowmobile's steerability. One skilled in the art describes this excessive “pushing ” as the sled being “too wheely” or having too “much rubber.”
One way the industry has attempted to deal with the concerns over pushing is by providing narrower ski stance for mountain snowmobiles than flatland snowmobiles, since narrowing ski stance generally tends to enhance the steerability of the sleds. Accordingly, a typical mountain sled is equipped with skis whose ski stance is in a range of about 37 inches to 39 inches, compared to the range of about 40 to 43 inches in the typical flatland snowmobiles.
Finally, flotation refers to the ability of the snowmobiles to stay “afloat” the terrain comprising mainly of fresh powdery snow. In contrast to the flatland trails where there is typically light snow on the ground, in the mountains, there may be hills and terrain which may be covered by as much as 5 to 6 feet of powdery snow. The design of the mountain snowmobiles must provide sufficient flotation on the powder snow as the sled is being driven on such hills and terrain. Typically, the floatability of a snowmobile is a function of many factors that includes the overall weight of the sleds and the overall surface area of the track contacting the snow surface.
Thus, conventional mountain sleds utilize “regular” tracks having a length of 136 inches to provide more snow contacting surface in comparison to the flatland sleds which generally favor the use of “short” tracks having a length of 121 inches. One notable exception of a flatland snowmobile having a track length greater than the 121 inch short track length is the utility snowmobile which may have a track longer than 136 inches, 156 inches for example. One of the key differences between a mountain snowmobile and a utility snowmobile, of course, lies in the height of the snow engaging lugs, which is substantially greater in tracks for the mountain sleds.
Notwithstanding the foregoing, many in the industry, until recently, used to hold the view that apart from the differences in the ski stance and the track length, the mountain snowmobiles are little different from the flatland snowmobiles. In the last few years, however, snowmobile manufacturers have devoted considerable attention to the mountain snowmobiles to satisfy the special requirements for use in the mountains.
There are several dimensional features of mountain snowmobiles that have been, by in large, constant and unchanging due to the requirements imposed by the specific driving conditions in the mountain applications. One of such dimensions is the aforementioned ski stance which is typically in a range of about 37 inches to 39 inches. Another of such dimensions is the length of the tracks for the mountain snowmobiles, which has been fixed at length of 136 inches. All mountain snowmobile made available by the snowmobile manufacturers heretofore have been made to use tracks having a length of 136 inches and no greater. If the end users wanted more traction or more snow contracting track surface, they needed to purchase an aftermarket track having a length of 141 inches and install using a bracket kit to accommodate the added length of 5 inches in the track.
The industry's adherence to a fixed track length of 136 inches reflects the magnitude of its concerns over “pushing.” Although greater traction and better flotation may have been achievable by lengthening the track length, those skilled in the art, however, have been reluctant to increase the length of the tracks for the snowmobiles. Many in the industry have been openly skeptical about whether mountain sleds having a track with a longer length than the industry standard 136 inches would properly function in mountain applications which also require an effective, satisfactory maneuverability. Such skepticism seemingly commanded much support from those skilled in the art, particularly in light of the fact that the snow engaging lugs have a height of about 1¼ to 2 inches. Although these gnarly lugs provide the necessary traction force to climb hills or to keep the sled moving in the deep powder snow, they run the risk of providing too great a traction force. The prevalent view in the industry was that the extra snow engaging lugs in combination with the increased track length would produce too much traction force and that the mountain sled would begin to loose steerability to negotiate around turns, because such “long length” tracks would push the mountain sled too much.
Largely because these concerns over “pushing” and “turning out,” one skilled in the art could not and did not change the length of the track, despite potential superior performance of the longer tracks in hill climbing capabilities and flotation. Indeed, such proclivity of the industry is evidenced by the fact that no major commercial manufacturer known to the applicants has made available a mountain snowmobile having a track whose length is greater than 136 inches. Further, even in the aftermarket, no track for mountain snowmobiles has a length greater than 141 inches prior to the present invention.
In efforts to improve upon the currently available mountain snowmobiles, the inventors desired to provide a track whose length is greater than the standard 136 inches and the 141 inches available in the aftermarket. While many in the industry have remained skeptical about using long tracks in mountain snowmobiles, the inventors determined that one of the avenues which could overcome the challenges of using the long tracks in mountain snowmobiles is to improve the tread patterns of the tracks. In particular, the inventors of the present invention focused on the relationship between the tread patterns and the nominal length of the tracks with respect to traction, maneuverability, and flotation.
As would be understood by one skilled in the art, a pitch is a traverse row along reinforcing means provided in the track. A particular arrangements of lugs on a pitch is defined herein as a pitch pattern. An arrangement of pitch patterns over a predetermined number of successive pitches is defined herein as a tread pattern, which repeated identically on the track on successive pitches. The arrangement of the tread patterns over the entire longitudinal length of the track is defined as a track pattern.
Significant research efforts have been devoted to improving and optimizing the characteristics of the tracks for snowmobiles, examples of which include: tread patterns disclosed in U.S. Pat. No. 5,713,645 to Thompson et al., and the tread pattern shown in FIG. 12, manufactured by Camoplast Inc. of Sherbrooke, Canada, Track Number 570-2109 and marketed by Bombardier Inc. of Montreal Canada as the track for a snowmobile under the trademark SKI-DOO, model 2000 Summit 700, model year 1999, shown in FIG. 11. While these noted examples provide effective traction and control of the snowmobile in many applications, the inventors of the present invention have found that still further improvements can be made in optimizing and improving the performance of the tracks, in particular for tracks for use on light or powder snow.
With the existing track profile configurations, when the snowmobile is operating on soft or powder snow, when there is increased traction force, the tracks may tend to simply dig a hole in the snow rather than propelling the sled in the driving direction. That is, given the state of the modern day high powered snowmobiles, under certain circumstances, the tracks with the existing track patterns would provide too much traction force vis-à-vis the steerability of the sleds, i.e., “too much rubber.” The most clear example of this shortcoming of the existing track configurations is evident when one attempts to use a long length track in a mountain snowmobile with the conventional track pattern.
As discussed earlier, mountain snowmobiles require the height of the lugs formed on the exterior surface of the track to be at least about 1¼ inches. The current trend is to provide 2-inch or 1¾ inch lugs for tracks for premium quality mountain snowmobiles. At the same time, when the inventors attempted increasing the traction force provided to the snowmobile by lengthening the nominal length of the track from the regular length of 136 inches to 151 inches, the traction force became too large for the snowmobile to maintain its steerability. Thus the requisite maneuverability of the snowmobile necessary in negotiating turns in the mountains was lost.
Thus, the inventors sought a novel track pattern which can advantageously improve the performance of a snowmobile on powder snow. This novel track would also enable the inventors to provide a mountain snowmobile having a long track whose length is greater than 136 inches, which is what the snowmobile manufacturers use, and also greater than 141 inches, which is what aftermarket track manufacturers make available. In that process, the inventors have further found that the novel track pattern surprisingly provides better track performance not only in the mountain snowmobiles, but also other types of snowmobiles, such as flatland snowmobiles.